The invention relates generally to sports shoes or boots and more particularly to a stud-shaped gripping element for such a shoe or boot. For the sake of simplicity herein, the term sports shoe will be used to denote any appropriate form of sports shoe, sports boot (being generally of a heavier construction than a sports shoe in the narrow sense), and the like. Further for the sake of simplicity herein the term gripping stud will be used in this specification to denote gripping elements which are used in particular on sports shoes for games played on a field or like surface and which are commonly referred to as studs or dogs. The invention is therefore not intended to cover gripping elements which are used on running shoes, in the form of spikes.
Many different forms of gripping studs for sports shoes have already been put forward, which comprise a stud body in combination with a ceramic insert which is connected to the stud body, for example by being secured to the lower end of a central metal portion thereof, and which forms the ground-engaging surface of the gripping stud. The ceramic inserts may comprise for example aluminium oxide, silicon carbide, tungsten carbide and the like, and the purpose thereof is substantially to increase the length of the service life of the gripping studs by making use of the very high level of resistance to wear of ceramic materials, while also avoiding the formation of sharp edges and nicks or notches on the gripping studs, which are produced due to wear thereof and which are a source of possible injury to players. Hitherto however it has not been possible for such gripping studs to be put to proper practical use because it has not been possible for the ceramic insert to sufficiently firmly connected to the body of the gripping stud, that the connection between the ceramic insert and the stud body is capable of securely withstanding the forces which act thereon in use of the sports shoe, while on the other hand it has not been possible to hold the manufacturing costs at a sufficiently low level that a ceramic-insert gripping stud is actually worthwhile, in comparison with gripping studs of the conventional configuration. Thus, in relation to a gripping stud as disclosed in German laid-open application (DE-OS) No. 32 33 900, an oxide ceramic insert which is of a frustoconical configuration at its top side is injected directly into the stud body which comprises plastic material, or is fixed in position thereon by adhesive means. Practical experience has shown however that that kind of connection between the ceramic inset and the stud body is not capable in the long term of withstanding in particular the thrust forces which act on the stud perpendicularly to the longitudinal axis thereof and which occur for example when the sports shoe on which the stud is fitted is subjected to a lateral loading on hard ground, so that the ceramic inserts come loose and may rapidly be lost. On the other hand, another form of stud element does not have specific ceramic insert but is made in its entirety from ceramic material. The ceramic stud is increased in width at its upper end, being the end which is towards the sole of the sports shoe on which the stud is fitted, so that the stud in that region forms a flange-like configuration which is embedded into a support member comprising glass fibre-reinforced or carbon fibre-reinforced polyamide and is thereby anchored to the sole of the sports shoe.
That design of gripping stud is so complicated and therefore expensive that the design in question cannot be considered for a gripping stud which is to be sold as a low-cost item.
In another form of gripping stud, the stud comprises a stud body having a central metal portion and a base portion which is disposed around the metal portion and which may comprise plastic material. A ceramic insert which forms the ground-engaging surface of the stud element is connected directly to the lower end of the metal portion, being the end which is away from the sole of the sports shoe to which the stud is fitted, with the connection between the ceramic insert and the metal portion being made by adhesive or soldering. A stud structure of that kind is disclosed for example in British patent specification No. 1 277 684. In that stud the ceramic insert is in the form of a ball which is fixed in a recess at the lower end of the metal portion of the stud body. Although that stud provides the advantage of a substantially enhanced level of resistance to abrasive wear, the ball configuration used for the ceramic insert is very sensitive to impact spot loadings due to the brittleness of the ceramic material so that it has a pronounced tendency for pieces of ceramic material to splinter or break away from the stud when the person wearing the sports shoe having the stud walks on a hard surface such as concrete.